What's the Windows Server 2003 Volume Shadow Copy Service (VSS)?

A. Windows 2003 includes several new file system features, such as enhanced DFS closest-site selection, the Virtual Disk Service, and Automated System Recovery (ASR). The most useful new feature is VSS.

Local Windows file systems include the Recycle Bin on the desktop, from which you can recover a deleted file. However, you can't recover deleted files on network shares unless you install third-party software. One thing VSS does is replcate the Recycle Bin for the network.

At configurable intervals, VSS takes a snapshot (aka Shadow Copy) of the state of content stored on selected volume shares. VSS stores only the changes for the shares, not the entire share content. For example, if you make a small change to a 5GB file, VSS stores only information about the change. The service stores as many as 64 versions of a share, depending on disk space. When the service creates the 65th Shadow Copy (or if you've used all the disk space allotted for Shadow Copies), the service deletes the oldest snapshot to make space for the newest snapshot. You can enable Shadow Copies only on NTFS volumes; you can't enable them for FAT volumes.

To enable Shadow Copies, clients install a software component that adds a Previous Versions tab to the Properties dialog box for the shares you want to Shadow Copy. Uses can select this tab to obtain a point-in-time view of the share and access its content. This functionality is great for users and administrators. If a user deletes a file or a file becomes corrupted, the user can simply view a version of the share that precedes the deletion or corruption and recover the file without troubling the administrator.

VSS doesn't replace backups, because the service stores only file changes--if you lose your file systems, the Shadow Copy information would be of no use. Microsoft has also stated that during times of exceptionally high I/O, Shadow Copies might be lost, so you shouldn't rely on VSS during critical-use times.

The amount of disk space required for Shadow Copies is based on the size and frequency of the file changes, which are driven by the applications used. For example, if an application writes only changes to a file when the file is modified, that application's changes will require far less Shadow Copy space than will an application that rewrites the entire file.

When you access a Shadow Copy, the file and folder ACLs still apply. Therefore, if you didn't have access to a particular file before, you won't have access to the file when you view the Shadow Copy. Windows 2003 stores information about the actual Shadow Copy file or folder in the System Volume Information of the volume that holds the Shadow Copy information, and this information isn't accessible.

Finally, although VSS protects the entire contents of a particular volume, you must use the share properties to view previous states of each volume share. Therefore, if you need to recover a file that isn't listed under a share, you must create a new share that contains the file, then connect to that share. (If you create a new share, you'll see a full history of the entire drive because VSS logs the entire file system, not just existing shares.)

Discuss this Article 14

It may be a great idea to some, however, using Tivoli as a backup app, the Open File Support does not work and shadow copy is given as the reason. I am trying to get rid of it to see if other "issues" show up.

Very useful but very dangerous! If you've got 100 users accessing a huge drive, one user who has access to everything could revert the whole drive back to a previous version. This would cause chaos in our company. Best if Administrators handle the restores.

OK. I just have to say that thing works on win2000 client but administrator must install ShadowCopyClient.msi on the client and allso same ShadowCopyClient.msi on the server 2003. Other OS didn't support.

Your Comments (required):This article doesn't talk about the fact that it really doesn't work in non-XP clients. I've tried numerous Win2k and 98 machines and I've been able to only get the client sw to work on XP.